Chinch Bugs Becoming Resistant To Pesticides

September 27, 1985|By Joan Brookwell, Gardening Editor

Robert Pardo calls it ``the famous chinch bug`` and says it is the biggest problem in Florida lawns.

Infamous is a better word for this small insect, which sucks the sap from grass blades and turns large patches of a lawn dry and brown. Chinch bugs do the most damage during hot, dry periods, and the first place damage usually shows up is near a sidewalk or driveway where soil dries up most rapidly.

When your lawn develops a large brown area, chinch bugs are probably the culprits. But you won`t find them in that dead area. ``They want the green stuff,`` says Pardo, urban horticulturist with the Broward County Cooperative Extension Service. You`re more likely to find them at the edge of the damaged spot. Pardo suggests you cut both ends from a can, push it into the lawn where green and brown grass meet, and fill the can with water. If chinch bugs are present they`ll float to the surface. If you don`t see them on the first try, move the can to several other spots.

When large numbers of the insects are present, they can be seen crawling on the grass blades. The adults have white winglike structures; the immature nymphs are lighter and have a red stripe across the top. Chinch bugs have a six-to-eight-week life cycle and can produce five generations a year.

Diazinon and dursban, which are organophosphates, are the pesticides most commonly used against chinch bugs, but the insects are becoming resistant to these chemicals. If 99 percent are killed, the 1 percent that survive produce offspring which also may be resistant, and succeeding generations get progressively hardier, Pardo says.

Baygon, a carbamate chemical, gives better control and the bugs seem to have developed little or no resistance to it. It is quite expensive, however. Pardo says insecticide granules last longer in the grass than a liquid, which leaches out quickly.

The chinch bug may be Lawn Enemy No. 1, but he`s not the only critter hanging around. Pardo says almost every home lawn has nematodes, for instance, and there is no good chemical to control them.

And there are more:

(BU) Sod webworms are the larvae of a tiny moth which feeds at night and thus is seldom seen. ``They hang around bushes during the day and come out at night and drop eggs like a B-52,`` says Pardo. The eggs develop into gray-green, black-spotted larvae which also are night feeders. They make holes in grass blades, leaving telltale sawdustlike droppings.

(BU) Mole crickets (two species -- southern and tawny) tunnel an inch or two below the soil surface, eating roots and uprooting the grass. ``They like nice wet soil, when it`s easy for them to go all over the place, doing their damage,`` Pardo says. A mole cricket will lay 30 to 35 eggs at a time in cavities in the sod.

Because Bahia grass is looser and more open than St. Augustine, it is a favorite target for mole crickets. Baits, sprays or granular insecticides are formulated for these pests and all work fairly well, Pardo says. Bait should be applied at dusk, because they feed mainly at night.

To find out if you have mole crickets, mix a teaspoon of detergent to a gallon of water and drench an area of lawn. If they are there, they`ll float to the surface.

(BU) Grubs are the immature stage of various beetles. They feed on grass roots throughout the day, staying beneath the soil surface. ``If you see one or two don`t worry about it, but if you have five or six per square foot you definitely have a problem,`` Pardo says. Diazinon or dursban should take care of them.

(BU) Fall armyworms and grass loopers, like other caterpillars, feed on leaf blades. Both are fairly large worms. Despite its name the fall armyworm does most of its damage in the early spring. But it`s not a major problem. Grass loopers do similar damage but all year long. They feed on grass blades during the day.

(BU) Billbugs, spittle bugs and scale are other pests that may attack grass, but they are not common in Florida.

Various diseases also damage lawns. Most, however, are fungal, and most fungus won`t kill a healthy lawn, Pardo says.

``We don`t recommend much chemical control for fungus,`` he says. ``Rely more on cultural practices. Spend your money on fertilizer, not fungicide.``

(BU) Pythium or root rot, which also occurs on trees and shrubs, is caused by too much water, especially in shady areas. Roots decay, leaving a white, cottony material which gives the disease the common name of cottony blight.

Reduce moisture, set the mower blades higher, and rake and bag clippings where it occurs to avoid spreading it. You may also use a fungicide such as Subdue 2E or another product with daconil. Avoid using fungicide in rainy weather. ``If you put daconil on this morning and it rains in the afternoon the daconil is gone, and with it your $10 or $20,`` Pardos says.